[Comparative study of production and control processes of parenteral nutritional admixtures in neonatology]. / Étude comparative des processus de production et de contrôle analytique des préparations magistrales de mélanges nutritifs parentéraux en néonatalogie.

OBJECTIVES: To assess the impact of disparities in production and analytical control processes on the quality of parenteral nutrition (PN) preparations produced in the Auvergne-Rhône-Alpes region. METHODS: This study was carried out in four hospital pharmacies of the Auvergne-Rhône-Alpes region. To assess the impact of production processes, each centre produced ten PN preparations from the same prescription. Analytical controls (sodium, potassium and calcium dosage) were carried out on all the preparations. To assess the impact of the control processes, a batch of ten preparations was produced from the same prescription. Samples were sent to the four hospital pharmacies for analytical control (sodium, potassium and calcium dosage). RESULTS: Measurements of relative production bias show that there is a significant difference between the preparations from the four centres in terms of sodium and potassium content. Each centre had at least one production bias for one of the three electrolytes measured. Concerning analytical controls, there was a significant difference between the four centres in the sodium and potassium levels measured. With the exception of calcium, all the centres reported measurements within the usual specifications of±10% of the target value. The results obtained have no clinically significant impact. CONCLUSION: The diversity of NP practices has a real impact on the quality of the preparations made. A regional collaboration should be envisaged to standardise patient care.

Automation of parenteral nutrition: impact on process and cost analysis.

OBJECTIVES: On the basis of its safety and accuracy, automation is recommended for parenteral nutrition (PN). The aim of this study was to highlight the changes in practices related to the automation of PN and to perform a cost study comparing manual vs automated production costs. METHODS: We conducted a micro-costing study using 1 year of manual production data for adult, neonatal and paediatric PN bagsat a hospital. We used the data to estimate the costs of automating the production process for adult, neonatal and paediatric bags. RESULTS: Major modification to the PN production process resulted in: rationalisation of raw materials, computerisation and optimisation of human needs. Switching from a manual to an automated process reduced the cost of neonatal/paediatric custom bags (€130.73 vs €124.58) and semi-custom bags (€172.08 vs €166.86); but increased the cost of adult bags (€93.06 vs €127.92). CONCLUSIONS: The changes resulting from the automation and revision of the production process globally increased annual expenditures by approximately 9.7%. However, automation minimised the risk of misproduction, bag contamination, and led to a more secure production process that reduced risks incurred by the teams. In view of the gain in patient and staff safety (linked to the use of an automated compounding device) the moderate economic impact (<10%) should not deter the automation of PN production circuits.

Comparison of three automated compounding devices for parenteral nutrition according to four key technical tests.

OBJECTIVES: Automation of parenteral nutrition (PN) preparation is nowadays a recommended practice in order to reduce human errors and thus improve the safety and accuracy of the finished product. Other benefits of automation may include full documentation of preparation and a reduction in personnel requirements or staff injuries. The market of automation compounding presents different automated compounding devices (ACDs). The aim of this study is to compare the technical characteristics of ACDs by carrying out four specific challenges. METHODS: Three ACDs: Two piston pumps with ACD 1: MediMix Multi 4120R (Impromediform) and ACD 2: Mibmix Compounder C12 (Hemedis), and one peristaltic pump ACD 3: ExactaMix Compounder EM2400 (Baxter) were assessed in a pharmaceutical manufacturing unit within a controlled atmosphere area, under horizontal laminar flow hood (LFH) according to four tests: volumetric accuracy, flush volume, smoke test, and a production test with three configurations of PN bags. For this test, a PN bag was considered accepted when all quality controls (weight, molar concentration of sodium, potassium and calcium) were fulfilled. RESULTS: The maximum relative biases found for the different ACDs were heterogeneous. ACD 1 had the best volumetric accuracy with respect to supplier specifications and for extreme volumes (0.2 mL). Evaluation of the flushing volume allowed the validation of 50 mL volumes for ACD 1 and ACD 3. The smoke test was only conclusive for ACD 1 under a horizontal LFH. The percentage of PN bags accepted were 98.8% for ACD 1, 70% for ACD 2%, and 95.5% for ACD 3. CONCLUSION: This study compared three ACDs according to four relevant and specific tests. Based on the data acquired, we conclude that ACD 1 is the most accurate, has the lowest flushing volume, is suitable for use in a LFH, and achieves the best results in the production test.

Place of magistral preparations to continue the treatment if the drug is commercially stopped worldwide? A case report of a 10-year-old child with subacute sclerosing panencephalitis (SSPE) requiring inosiplex.

Subacute sclerosing panencephalitis (SSPE) is a late-onset and fatal viral disease caused by persistent infection of the central nervous system by measles virus (MeV). We present the case of a 10-year-old child from South Asia affected by SSPE, stabilized with a combination of intrathecal interferon-α2b (INF-α2b) injections and oral inosiplex and how we continued the treatment when inosiplex was commercially stopped worldwide.

Influence of the Immune Microenvironment Provided by Implanted Biomaterials on the Biological Properties of Masquelet-Induced Membranes in Rats: Metakaolin as an Alternative Spacer.

Macrophages play a key role in the inflammatory phase of wound repair and foreign body reactions-two important processes in the Masquelet-induced membrane technique for extremity reconstruction. The macrophage response depends largely on the nature of the biomaterials implanted. However, little is known about the influence of the macrophage microenvironment on the osteogenic properties of the induced membrane or subsequent bone regeneration. We used metakaolin, an immunogenic material, as an alternative spacer to standard polymethylmethacrylate (PMMA) in a Masquelet model in rats. Four weeks after implantation, the PMMA- and metakaolin-induced membranes were harvested, and their osteogenic properties and macrophage microenvironments were investigated by histology, immunohistochemistry, mass spectroscopy and gene expression analysis. The metakaolin spacer induced membranes with higher levels of two potent pro-osteogenic factors, transforming growth factor-ß (TGF-ß) and bone morphogenic protein-2 (BMP-2). These alternative membranes thus had greater osteogenic activity, which was accompanied by a significant expansion of the total macrophage population, including both the M1-like and M2-like subtypes. Microcomputed tomographic analysis showed that metakaolin-induced membranes supported bone regeneration more effectively than PMMA-induced membranes through better callus properties (+58%), although this difference was not significant. This study provides the first evidence of the influence of the immune microenvironment on the osteogenic properties of the induced membranes.

Masquelet technique in military practice: specificities and future directions for combat-related bone defect reconstruction.

Because of its simplicity, reliability, and replicability, the Masquelet induced membrane technique (IMT) has become one of the preferred methods for critical bone defect reconstruction in extremities. Although it is now used worldwide, few studies have been published about IMT in military practice. Bone reconstruction is particularly challenging in this context of care due to extensive soft-tissue injury, early wound infection, and even delayed management in austere conditions. Based on our clinical expertise, recent research, and a literature analysis, this narrative review provides an overview of the IMT application to combat-related bone defects. It presents technical specificities and future developments aiming to optimize IMT outcomes, including for the management of massive multi-tissue defects or bone reconstruction performed in the field with limited resources.

A quality by design approach for the qualification of automating compounding device for parenteral nutrition.

Automated compounding device (ACD) are increasingly used for parenteral nutrition (PN) bag production, and their acquisition must be sufficiently thought. The law requires the qualification of these ACD, but did not specify the tests to be performed. The quality by design (QbD) risk based approach allowed to define the quality target product profile in order to acquire the best ACD for each unit, and thanks a risk analysis permitted to define the critical quality attributes (CQA). These CQA will allowed to define tests performed during qualification. The ACD qualified was a 12 pump volumetric system. The CQA for PN bags consisted in sterile, precisely and accurately production with enough stability. During operational qualification volumetric accuracy test was performed, and during the performance qualification: flush volume, media fill, microbiological integrity of environment, sterility of control bag and production test were performed. At the end, all tests were conclusive (excepted for some results mostly due to analytical bias) and the ACD was considered to produce sterile bags in a control environment, precisely (relative standard deviation < 4%) and accurately (mean bias < 1% for weight and < 7% for other controls) with a sufficient stability. The QbD risk based approach allowed to acquire the best ACD for our need, and qualify relevant elements regarding the production process.

Macrophages Characterization in an Injured Bone Tissue.

Biomaterial use is a promising approach to facilitate wound healing of the bone tissue. Biomaterials induce the formation of membrane capsules and the recruitment of different types of macrophages. Macrophages are immune cells that produce diverse combinations of cytokines playing an important role in bone healing and regeneration, but the exact mechanism remains to be studied. Our work aimed to identify in vivo macrophages in the Masquelet induced membrane in a rat model. Most of the macrophages in the damaged area were M2-like, with smaller numbers of M1-like macrophages. In addition, high expression of IL-1ß and IL-6 cytokines were detected in the membrane region by RT-qPCR. Using an innovative combination of two hybridization techniques (in situ hybridization and in situ hybridization chain reaction (in situ HCR)), M2b-like macrophages were identified for the first time in cryosections of non-decalcified bone. Our work has also demonstrated that microspectroscopical analysis is essential for macrophage characterization, as it allows the discrimination of fluorescence and autofluorescence. Finally, this work has revealed the limitations of immunolabelling and the potential of in situ HCR to provide valuable information for in vivo characterization of macrophages.

In Situ Gene Expression in Native Cryofixed Bone Tissue.

Bone is a very complex tissue that is constantly changing throughout the lifespan. The precise mechanism of bone regeneration remains poorly understood. Large bone defects can be caused by gunshot injury, trauma, accidents, congenital anomalies and tissue resection due to cancer. Therefore, understanding bone homeostasis and regeneration has considerable clinical and scientific importance in the development of bone therapy. Macrophages are well known innate immune cells secreting different combinations of cytokines and their role in bone regeneration during bone healing is essential. Here, we present a method to identify mRNA transcripts in cryosections of non-decalcified rat bone using in situ hybridization and hybridization chain reaction to explore gene expression in situ for better understanding the gene expression of the bone tissues.

The Masquelet Technique: Can Disposable Polypropylene Syringes be an Alternative to Standard PMMA Spacers? A Rat Bone Defect Model.

BACKGROUND: Usually, the two-stage Masquelet induced-membrane technique for extremity reconstruction begins with a polymethylmethacrylate (PMMA) cement spacer-driven membrane, followed by an autologous cancellous bone graft implanted into the membrane cavity to promote healing of large bone defects. In exceptional cases, spacers made of polypropylene disposable syringes were successfully used instead of the usual PMMA spacers because of a PMMA cement shortage caused by a lack of resources. However, this approach lacks clinical evidence and requires experimental validation before being recommended as an alternative to the conventional technique. QUESTIONS/PURPOSES: To (1) develop and (2) validate a critical-sized femoral defect model in rats for two stages of the Masquelet technique and to (3) compare the biological and bone healing properties of polypropylene-induced membranes and PMMA-induced membranes in this model. METHODS: Fifty male Sprague Dawley rats aged 8 weeks old received a 6-mm femur defect, which was stabilized with an external fixator that was converted into an internal device. In the development phase, the defect was filled with PMMA in 16 rats to determine the most favorable timing for bone grafting. Two rats were excluded since they died of anesthetic complications. The other 14 were successively euthanized after 2 weeks (n = 3), 4 weeks (n = 4), 6 weeks (n = 4), and 8 weeks (n = 3) for induced membrane analyses. In the validation phase, 12 rats underwent both stages of the procedure using a PMMA spacer and were randomly assigned to two groups, whether the induced membrane was preserved or removed before grafting. To address our final objective, we implanted either polypropylene or PMMA spacers into the defect (Masquelet technique Stage 1; n = 11 rats per group) for the period established by the development phase. In each group, 6 of 11 rats were euthanized to compare the biological properties of polypropylene-induced membranes and PMMA-induced membranes using histological qualitative analysis, semiquantitative assessment of the bone morphogenic protein-2 content by immunostaining, and qualitative assessment of the mesenchymal stromal cell (MSC; CD31-, CD45-, CD90+, and CD73+ phenotypes) content by flow cytometry. Quantitative measurements from serum bone turnover markers were also performed. The five remaining rats of each group were used for Masquelet technique Stage 2, in which rat bone allografts were implanted in the induced membrane cavity after the polypropylene or PMMA spacers were removed. These rats recovered for 10 weeks before being euthanized for microCT quantitative measurements and bone histology qualitative assessment to evaluate and compare the extent of bone regeneration between groups. RESULTS: Induced membrane analyses together with serum bone turnover measurements indicated that a 4-week interval time between stages was the most favorable. Removal of the induced membrane before grafting led to almost constant early implant failures with poor bone formation. Four-week-old rats with polypropylene-triggered induced membranes displayed similar histologic organization as rats with PMMA-driven induced membranes, without any difference in the cell density of the extracellular matrix (4933 ± 916 cells per mm2 for polypropylene versus 4923 ± 1284 cells per mm2 for PMMA; p = 0.98). Induced membrane-derived MSCs were found in both groups with no difference (4 of 5 with polypropylene versus 3 of 3 with PMMA; p > 0.99). Induced membrane bone morphogenic protein-2 immunolabeling and serum bone turnover marker levels were comparable between the polypropylene and PMMA groups. MicroCT analysis found that bone regeneration in the polypropylene group seemed comparable with that in the PMMA group (29 ± 26 mm3 for polypropylene versus 24 ± 18 mm3 for PMMA; p > 0.99). Finally, qualitative histological assessment revealed a satisfactory endochondral ossification maturation in both groups. CONCLUSION: Using a critical-sized femoral defect model in rats, we demonstrated that polypropylene spacers could induce membrane encapsulation with histologic characteristics and bone regenerative capacities that seem like those of PMMA spacers. CLINICAL RELEVANCE: In a same bone site, polymers with close physical properties seem to lead to similar foreign body reactions and induce encapsulating membranes with comparable bone healing properties. Polypropylene spacers made from disposable syringes could be a valuable alternative to PMMA. These results support the possibility of a cementless Masquelet technique in cases of PMMA shortage caused by a lack of resources.

Induced membrane technique: a critical literature analysis and proposal for a failure classification scheme.

The reconstruction of long-bone segmental defects remains challenging, with the three common methods of treatment being bone transport, vascularized bone transfer, and the induced membrane technique (IMT). Because of its simplicity, replicability, and reliability, usage of IMT has spread all over the world in the last decade, with more than 300 papers published in the PubMed literature database on this subject so far. Most of the clinical studies have reported high rates of bone union, yet some also include more controversial results with frequent complications and revision surgeries. At the same time, various experimental research efforts have been designed to understand and improve the biological properties of the induced membrane. This literature review aims to provide an overview of IMT clinical results in terms of bone union and complications and to compare them with those of other reconstructive procedures. In light of our findings, we then propose an original classification scheme of IMT failures distinguishing between preventable and nonpreventable failures.

Repeated Induced-Membrane Technique Failure without Infection: A Series of Three Consecutive Procedures Performed for a Single Femur Defect.

A 40-year-old male was treated using the induced-membrane technique (IMT) for a noninfected, 9 cm long femoral bone defect complicating a lengthening procedure. The interesting case feature lies in the three consecutive IMT procedures that were necessary to achieve complete bone repair in this unusual clinical situation. The first procedure failed because of the lack of graft revascularization likely related to an induced-membrane (IM) alteration demonstrated by histological observations. The second IMT procedure led to partial graft integration interrupted by the elongation nail breakage. At last, the third procedure fully succeeded after nail exchange and iterative iliac bone grafting. Complete bone union was achieved with a poor functional recovery one year after the last procedure and four years following the first cement spacer implantation. By means of clinical and histological observations, we demonstrated that the first and the second IMT failures had two distinct origins, namely, biological and mechanical causes, respectively. Although simple, a successful IMT procedure is not so easy to complete.

Bone reconstruction by the induced membrane technique. What differences between conventional and ballistic trauma?

BACKGROUND: The induced membrane technique (IMT) has been widely evaluated for reconstruction of post-traumatic bone defects. However, no specific evaluation was conducted in ballistic injuries. The objective of the present study was to compare IMT in conventional trauma (CT) versus ballistic trauma (BT) managed in a military trauma center. METHODS: A retrospective study was conducted between 2009 and 2018 in patients treated by IMT for post-traumatic bone defects, whatever the defect location. Endpoints comprised bone union, residual infection, additional bone grafting and lower-limb amputation. RESULTS: Thirty-six patients were included: 24 in the CT and 12 in the BT group. Demographics and injury pattern were similar in both groups, with open fracture and infected lesions predominating. The only significant difference was that tibial bone defects were larger in the BT group. Operative parameters and results were also similar. At a mean 24 months' follow-up, bone union rate was 83% in both groups, without significant differences in residual infection, complementary grafting or late amputation. CONCLUSION: IMT is appropriate to bone reconstruction in the aftermath of ballistic trauma, with similar results to those obtained in conventional trauma. LEVEL OF EVIDENCE: IV, retrospective study.

Towards Understanding Therapeutic Failures in Masquelet Surgery: First Evidence that Defective Induced Membrane Properties are Associated with Clinical Failures.

The two-stage Masquelet induced-membrane technique (IMT) consists of cement spacer-driven membrane induction followed by an autologous cancellous bone implantation in this membrane to promote large bone defect repairs. For the first time, this study aims at correlating IMT failures with physiological alterations of the induced membrane (IM) in patients. For this purpose, we compared various histological, immunohistochemical and gene expression parameters obtained from IM collected in patients categorized lately as successfully (Responders; n = 8) or unsuccessfully (Non-responders; n = 3) treated with the Masquelet technique (6 month clinical and radiologic post-surgery follow-up). While angiogenesis or macrophage distribution pattern remained unmodified in non-responder IM as compared to responder IM, we evidenced an absence of mesenchymal stem cells and reduced density of fibroblast-like cells in non-responder IM. Furthermore, non-responder IM exhibited altered extracellular matrix (ECM) remodeling parameters such as a lower expression ratio of metalloproteinase-9 (MMP-9)/tissue inhibitor of metalloproteinases (TIMP-1) mRNA as well as an important collagen overexpression as shown by picrosirius red staining. In summary, this study is the first to report evidence that IMT failure can be related to defective IM properties while underlining the importance of ECM remodeling parameters, particularly the MMP-9/TIMP-1 gene expression ratio, as early predictive biomarkers of the IMT outcome regardless of the type of bone, fracture or patient characteristics.

Masquelet technique for open tibia fractures in a military setting.

PURPOSE: The induced membrane technique (IMT) is a two-stage procedure dedicated to reconstruction of bone defects of the limbs. The objective of this report was to evaluate employment of the IMT for the treatment of open tibia fractures managed in a military trauma center treating both wartime and peacetime injuries. METHODS: A retrospective study was performed among the patients treated via IMT for tibial bone defects related to open fractures between 2009 and 2018. The outcomes recorded included bone union, residual infection, amputation and lower limb function. RESULTS: During this period, 15 patients with a mean age of 39 years were included for the treatment of Gustilo II (2 cases) or Gustilo IIIB (13 cases) injuries. A mean number of 2.9 debridements were required before stage 1. Flap coverage was associated in 14 cases. The mean interval between stages was 22 weeks. Five patients were re-operated on after stage 1 due to persistent infection. The mean follow-up was 33 months. Bone union was achieved in 13 of the 15 cases (87%) at a mean time of 10.1 months. However, seven additional bone healing procedures were required, including six inter-tibiofibular grafting. Only one late septic recurrence was found. Most patients returned to work in sedentary jobs. CONCLUSIONS: This series is the first to report IMT use in a military setting. The prior eradication of infection constitutes a major challenge in tibial bone defects, especially in high-energy, multi-tissue injuries. An inter-tibiofibular bone reconstruction approach is required when external fixation is chosen.

Separate and combined effects of hypobaric hypoxia and hindlimb suspension on skeletal homeostasis and hematopoiesis in mice.

PURPOSE: Bone marrow response to an organismal stress is made by orchestrating the interplay between hematopoietic stem/progenitor cells (HSPCs) and mesenchymal stromal cells (MSCs). Neither the cellular nor the molecular factors that regulate this process are fully understood, especially since this mechanism probably varies depending on the type of stress. Herein, we explored the differentiation and fate of MSCs and HSPCs in mice challenged with a hematopoietic stress or a mechanical stress applied separately or in combination. METHODS: Mice were subjected to 4 days of hypobaric hypoxia (hematopoietic challenge) and/or 7 days of hindlimb suspension (stromal challenge) and then sacrificed for blood and bone collection. Using hematological measurements, colony-forming unit assays, bone histomorphometry and array-based multiplex ELISA analysis, we evaluated challenge influences on both MSC and HSPC mobilization, differentiation (osteoblasts, osteoclasts, and mature blood cells) and fate. RESULTS: We found that hypoxia leads to HSPC mobilization and that an imbalance between bone formation and bone resorption accounts for this mobilization. Whilst suspension is also associated with an imbalance between bone formation and bone resorption, it does not induce HSPC mobilization. Then, we revealed cellular interactions by combining hematopoietic and stromal challenges together in mice. We showed that the hypoxia-driven HSPC mobilization is moderated by suspension. Moreover, when applied in a hypoxic environment, suspension offsets bone imbalance. We identified stroma cell-derived factors MIP-1α, HGF and SDF-1 as potent molecular key players sustaining interactions between hindlimb suspension and hypobaric hypoxia. CONCLUSION: Taken together, our data highlight the benefit of combining different types of stress to better understand the interplay between MSCs and HSPCs.

Short-term Efficiency and Tolerance of Ketoprofen and Methylprednisolone in Acute Sciatica: A Randomized Trial.

OBJECTIVE: Although anti-inflammatory drugs are commonly used in acute discogenic sciatica, data regarding their efficacy are scarce and controversial. We compared the efficacy and safety of intravenous ketoprofen and methylprednisolone with placebo in sciatica. DESIGN: Multicenter, double-blinded randomized controlled trial. SUBJECTS: Patients with confirmed discogenic acute sciatica, without neurologic deficit, were randomized into three arms. METHODS: Besides standard-of-care analgesic therapy, they received intravenous injections of methylprednisolone (60 mg/d) or ketoprofen (200 mg/d) or placebo for five days. The primary outcome was leg pain over five days. Secondary outcomes were clinical responses at days 3 and 5, lumbar pain, Straight Leg Raise Test and lumbar flexion index, analgesic consumption, realization of lumbar spine injections, and surgery during the study period. RESULTS: Fifty-four patients were randomized, and 50 completed the study. In patients admitted to the hospital for pain control with acute lumbar radicular pain due to intervertebral disc herniation and receiving an oral analgesic protocol including paracetamol, nefopam, tramadol, and morphine, there was no additional analgesic effect seen between groups. There was no significant difference in leg pain between the three groups over the study period. In the methylprednisolone group, however, we observed a higher rate of clinically relevant responses at day 3. No difference was observed on other secondary efficacy outcomes and safety. CONCLUSION: No significant difference in leg pain was observed between groups. However, there was a higher proportion of patients relieved with intravenous methylprednisolone at day 3, compared with ketoprofen or placebo.

Simultaneous three-dimensional visualization of mineralized and soft skeletal tissues by a novel microCT contrast agent with polyoxometalate structure.

Biological tissues have a complex and heterogeneous 3D structure, which is only partially revealed by standard histomorphometry in 2D. We here present a novel chemical compound for contrast-enhanced microfocus computed tomography (CE-CT), a Hafnium-based Wells-Dawson polyoxometalate (Hf-POM), which allows simultaneous 3D visualization of mineralized and non-mineralized skeletal tissues, such as mineralized bone and bone marrow vasculature and adipocytes. We validated the novel contrast agent, which has a neutral pH in solution, by detailed comparison with (immuno)histology on murine long bones as blueprint, and showed that Hf-POM-based CE-CT can be used for virtual 3D histology. Furthermore, we quantified the 3D structure of the different skeletal tissues, as well as their spatial relation to each other, during aging and diet-induced obesity. We discovered, based on a single CE-CT dataset per sample, clear differences between the groups in bone structure, vascular network organization, characteristics of the adipose tissue and proximity of the different tissues to each other. These findings highlight the complementarity and added value of Hf-POM-based CE-CT compared to standard histomorphometry. As this novel technology provides a detailed 3D simultaneous representation of the structural organization of mineralized bone and bone marrow vasculature and adipose tissue, it will enable to improve insight in the interactions between these three tissues in several bone pathologies and to evaluate the in vivo performance of biomaterials for skeletal regeneration.

In vivo hypobaric hypoxia performed during the remodeling process accelerates bone healing in mice.

We investigated the effects of respiratory hypobaric hypoxia on femoral bone-defect repair in mice because hypoxia is believed to influence both mesenchymal stromal cell (MSC) and hematopoietic stem cell mobilization, a process involved in the bone-healing mechanism. To mimic conditions of non-weight-bearing limb immobilization in patients suffering from bone trauma, our hypoxic mouse model was further subjected to hind-limb unloading. A hole was drilled in the right femur of adult male C57/BL6J mice. Four days after surgery, mice were subjected to hind-limb unloading for 1 week. Seven days after surgery, mice were either housed for 4 days in a hypobaric room (FiO2 at 10%) or kept under normoxic conditions. Unsuspended control mice were housed in either hypobaric or normoxic conditions. Animals were sacrificed on postsurgery day 11 to allow for collection of both contralateral and lesioned femurs, blood, and spleen. As assessed by microtomography, delayed hypoxia enhanced bone-healing efficiency by increasing the closing of the cortical defect and the newly synthesized bone volume in the cavity by +55% and +35%, respectively. Proteome analysis and histomorphometric data suggested that bone-repair improvement likely results from the acceleration of the natural bone-healing process rather than from extended mobilization of MSC-derived osteoprogenitors. Hind-limb unloading had hardly any effect beyond delayed hypoxia-enhanced bone-healing efficiency.